Paint mixing machines have improved the ease of preparing paints, particularly when custom matching colors for individual paint orders. By using such paint mixers, a desired color or texture can be quickly and economically produced by store clerks or even the consumer by simply adding the predetermined quantity of the various colors to the base paint, and placing the paint container into the mixer. This procedure obviates the expense of mixing paint in large quantities using industrial type mixing machines, which require a significant amount of labor, time and skill. The new generation of paint mixers can be kept conveniently at the business of paint retailers who can immediately fill custom orders. The development of more automated mixing devices has resulted in a savings of time and reduced costs in producing paint, as well as convenience to consumers.
A common type of available paint mixers is the paint shaker, in which the paint container is placed within a shaking compartment and shaken until the contents have been sufficiently mixed. The paint container must be tightly secured into place before the shaking operation commences so that the shaking motion is transferred to the paint container and also to prevent spillage and potential damage to the paint container and mixing apparatus. Therefore, the proper and adequate securing of the paint container within a paint shaker is of great importance.
In the past, paint containers were manually secured and sealed through various mechanical locking devices, such as a clamping plate which is latched down onto the top of the container by the operator. Additionally, the operator could manually lower the electrically or pneumatically driven clamping plates by operating a switch until the clamping plate pressed down on the top of the paint container. These types of clamping devices required manual operation of the clamping device, requiring more time to operate the machine and more skill of the operator who had to judge at what point the paint container was sufficiently secured without possibly crushing the container and damaging the seal.
Automatic clamping devices were developed to make securing the paint container easier, but suffer from certain disadvantages which render them less efficient. One such automatic clamping device is shown in U.S. Pat. No. 4,134,689 which includes two vertically aligned and parallel threaded rods, a clamping plate with two threaded openings to receive the rods, a drive-belt, and an electric motor. The two rods are linked axially by a drive-belt at the top end, allowing the two rods to rotate in unison when either rod is driven by an electric motor. The rotation of the two rods screws and unscrews the clamping plate up or down to secure the paint container. Additionally, a voltage sensor detects when the clamping plate is pushed against the container top to shut off the electric motor.
One drawback in this design is the time required to raise and lower the clamping plate because the vertical movement of the clamping plate is effected by screwing motions. The additional time becomes most apparent when dealing with containers of varying sizes and when many paint containers require mixing. Because the clamping plate is indirectly moved through a screwing motion, as opposed to a direct vertical force onto the clamping plate, more energy is expended to create the vertical movement of the clamping plate. Furthermore, the frictional resistance in the numerous moving contact points in this type of dual rod drive-belt assembly presents a source of wasted energy and loss of efficiency. Loss of efficiency is inherent in such a dual rod clamping apparatus due to the numerous moving parts and frictional contact surfaces required. Additionally, any slippage in the drive belt connecting the two rods will result in an asynchronous axial rotation of the two thread rods, resulting in a non-horizontal clamping plate. If the clamping plate becomes angled, or non-horizontal, the downward force of the clamping plate would concentrate on one point on the edge of the container rather than evenly over the entire surface of the container. This problem, depending on the downward force generated, could result in crushing the paint container and spillage of the paint within the paint shaker. Even if the container withstands the irregularly angled force exerted by the non-horizontal clamping plate, the container may not be properly secured and might loosen after the shaking begins, creating a dangerous condition for the operator and potential liability for the paint retailer supplying the paint mixing machine.